Development spectrophotometric methods for determination of some drug active substances

In this study, sensitive, easy and selective spectrophotometric methods for the determination of Carvedilol, Nebivolol HCl and Paroxetine HCl from tablet dosage forms were developed. The method developed for carvedilol is based on a charge transfer reaction with 1,2,5,8-tetrahydroxythraquinone (quinalizarin). The method was optimized by examining the effect of type of solvent, Quinalizarin concentration, reaction of time and temperature on the absorbance. The stoichiometric ratio of the charge transfer complex was determined by the Job method. The methods developed for Nebivolol HCl and Paroxetine HCl are based on the formation of a colored Cu-drug-dithiocarbamate complexes on the basis of the secondary amine group in the structures of both drugs. In the first stage of the study, the drug substances were converted into dithiocarbamate derivatives with CS2 in basic medium. Then, brown complexes from the dithiocarbamate derivatives were formed by adding Cu2+ to the medium. In the second step the complexes formed were extracted into an organic solvent phase from water phase. The methods were optimized by examining effect of type of solvent, NH3 concentration, CS2 concentration, Cu2+ concentration on the absorption for both drugs. After optimum conditions were determined for three drugs, the methods were statistically validated and the developed methods were successfully applied to the tablet formulations of the drugs.